Much research and development work about antitumor agents have been made and clinically various excellent antitumor agents are in use for the chemotherapy of malignant tumors. The outcomes of such therapies have been improved year after year but the efficacies are only transitory in many instances and are not necessarily sufficient to arrest growth of tumors and assure patients of long life spans. By way of illustration, tegafur is a substance which is activated in the living body to release 5-fluorouracil (hereinafter referred to as 5-FU), the substance of its antitumor activity, and was designed to alleviate the toxicity or adverse effect of 5-FU. The advent of a combination drug consisting of tegafur and uracil is predicated on the idea that while 5-FU is rapidly metabolized and loses its activity in the body, this inactivation is inhibited by uracil which has no antitumor activity of its own to thereby achieve a marked potentiation of the antitumor effect.
However, the current status of cancer therapy points to the need for development of drugs having higher antitumor activity.